Data centers are often used by service providers to deliver Internet based services to users. A data center, such as a server farm, typically contains hundreds or thousands of processing devices. Within the data centers the processing devices are arranged (or grouped) in clusters. Each cluster is configured to perform a distributed task in a parallel or pipelined fashion. Clusters may be logically or physically defined.
Because there are typically many thousands of processing devices in a data center, the data centers have large energy requirements. These requirements are often on the order of megawatts. The energy consumption of a data center contributes a significant fraction to the total operational costs of running the data center.